Maximum likelihood error detection for decision feedback equalizers with PAM modulation

ABSTRACT

The present invention is directed to data communication. More specifically, an embodiment of the present invention provides an error correction system. Input data signals are processed by a feedforward equalization module and a decision feedback back equalization module. Decisions generated by the decision feedback equalization module are processed by an error detection module, which determines error events associated with the decisions. The error detection module implements a reduced state trellis path. There are other embodiments as well.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 16/515,895, filed on Jul. 18, 2019, which is acontinuation of U.S. patent application Ser. No. 15/995,036, (now U.S.Pat. No. 10,404,289, issued on Sep. 3, 2019) filed on May 31, 2018,commonly assigned and incorporated by reference herein for all purposes.

BACKGROUND OF THE INVENTION

The present invention is directed to data communication.

Over the last few decades, the use of communication networks hasexploded. In the early days of the Internet, popular applications werelimited to emails, bulletin board, and mostly informational andtext-based web page surfing, and the amount of data transferred wasrelatively small. Today, the Internet and mobile applications demand ahuge amount of bandwidth for transferring photo, video, music, and othermultimedia files. For example, a social network like Facebook processesmore than 500 TB of data daily. With such high demands on data storageand data transfer, existing data communication systems need to beimproved to address these needs.

Error detection and correction is an important aspect of datacommunication. For example, feedforward equalization and decisionfeedback equalization are useful techniques, and various conventionalcommunication systems used them. Unfortunately, conventional systems andtechniques have been inadequate. Therefore, new and improved errorcorrection techniques are desired.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to data communication. Morespecifically, an embodiment of the present invention provides an errorcorrection system. Input data signals are processed by a feedforwardequalization module and a decision feedback equalization module.Decisions generated by the decision feedback equalization module areprocessed by an error detection module, which determines error eventsassociated with the decisions. The error detection module implements areduced state trellis path. There are other embodiments as well.

According to an embodiment, the present invention provides an errordetection device, which includes an input terminal for receiving a datasignal. The device further includes a feedforward equalization (FFE)module configured to equalize the data signal and generate an equalizeddata signal. The device also includes a first decision feedbackequalization (DFE) module configured to remove at least intersymbolinterference (ISI) noises from the equalized data signal and generateDFE decisions. The device additionally includes an error detectionmodule configured to detect error events associated with the DFEdecisions by performing maximum likelihood detections. The errordetection module is configured to store signs associated with an inputerror state and generate an output error state by flipping the signs.The FFE module amplifies an amplitude of the data signal by apredetermined amount. The error detection module removes burst errorsassociated with the DFE decisions. The device further comprises areflection cancelation module coupled to the first DFE module forremoving reflection noises. In various implementations, the data signalcomprises PAM4 data. The device may further include a slicer module forprocessing the equalized data signal. For example, the error events areassociated with Nyquist error events (i.e., alternating-sign errorevents).

According to another embodiment, the present invention provides an inputterminal for receiving a data signal. The device includes a feedforwardequalization (FFE) module configured to equalize the data signal andgenerate an equalized data signal. The device also includes a decisionfeedback equalization (DFE) module configured to remove intersymbolinterference (ISI) noises from the equalized data signal and generateDFE decisions. The device additionally includes an error generatormodule configured to generate an error signal by comparing the equalizeddata and the DFE decisions further includes an error detection moduleconfigured to detect error by analyzing the DFE decisions and the errorsignal. The error detection module is configured to store signsassociated with an input error state and generate an output error stateby flipping the signs. In a specific embodiment, the error detectionmodule comprises a maximum likelihood sequence detection module. In anembodiment, the error generator subtracts DFE decisions from theequalized data signal. In an implementation, the device additionallyincludes a non-linear cancelation module. In an embodiment, the errordetection module implements a reduced-state trellis path, where thereduced-state trellis path comprises an input zero state and the inputerror state, and the reduced-state trellis path also includes an outputzero state and the output error state.

According to yet another embodiment, the present invention provides acommunication device that includes an input terminal for receiving adata signal. The device also includes a feedforward equalization (FFE)module configured to equalize the data signal and generate an equalizeddata signal. The device additionally includes a decision feedbackequalization (DFE) module configured to remove intersymbol interference(ISI) noises from the equalized data signal and generate DFE decisions.The device further includes an error detection module configured todetect error events associated with the DFE decisions by performingmaximum likelihood detections. The error detection module is configuredto store signs associated with an input error state and generate anoutput error state by flipping the signs. The device additionallyincludes a forward error correction (FEC) decoder for decoding theequalized data signal using at least the DFE decision. In a specificembodiment, the FFE module amplifies an amplitude of the data signal bya predetermined amount. In certain embodiments, the device furtherincludes a de-mapping module coupled to the FEC decoder. In a specificembodiment, the device also includes a slicer module coupled to the FFEmodule. The device may also include a control module coupled to the DFEmodule.

It is to be appreciated that embodiments of the present inventionprovide many advantages over conventional techniques. Among otherthings, the MLSD can effectively reduce errors in DFE decisions, therebyimproving system performance. In various embodiments, MLSD techniquestake advantage of prior knowledge in DFE decisions and implementstrellis path with a reduced number of states. For example, embodimentsof the present invention provide an error-event MLSD (ee-MLSD). As anexample, ee-MLSD is implemented as a post-processing unit cleaning DFEerrors. Compared to conventional full-fledged MSLDs, ee-MLSDsimplemented with reduced-states can provide substantially the sameaccuracy, but at a much lowered costs.

Embodiments of the present invention can be implemented in conjunctionwith existing systems and processes. For example, an error correctionmodule can be implemented using existing hardware modules, which can bemanufactured using conventional equipment and techniques. Additionally,different detection and equalization schemes such as decision feedbackequalization, reflection cancelation, slicer, maximum likelihooddetection, and/or others—can be implemented to complement the subsequenterror correction system to provide a high level of flexibility intrading off power for performance. There are other benefits as well.

The present invention achieves these benefits and others in the contextof known technology. However, a further understanding of the nature andadvantages of the present invention may be realized by reference to thelatter portions of the specification and attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is directed to data communication. Morespecifically, an embodiment of the present invention provides an errorcorrection system. Input data signals are processed by a feedforwardequalization module and a decision feedback back equalization module.Decisions generated by the decision feedback equalization module areprocessed by an error detection module, which determines error eventsassociated with the decisions. The error detection module implements areduced state trellis path. There are other embodiments as well.

FIG. 1A is a simplified block diagram illustrating an error correctionsystem according to embodiments of the present invention.

FIG. 1B is a simplified diagram illustrating a communication systemaccording to embodiments of the present invention.

FIG. 1C is a simplified diagram illustrating an error detection moduleaccording to embodiments of the present invention.

FIG. 1D is a simplified diagram illustrating an error detection modulewith an enable logic according to embodiments of the present invention.

FIG. 2 is a simplified state diagram illustrating a trellis statediagram according to embodiments of the present invention.

FIG. 3 is a simplified state diagram illustrating a simplified trellisT₁ state diagram according to embodiments of the present invention.

FIG. 4 is a simplified diagram illustrating an ee-MLSD according to anembodiment of the present invention.

FIG. 5 is a graph illustrating simulation results comparing performanceof ee-MLSD devices according to embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to data communication. Morespecifically, an embodiment of the present invention provides an errorcorrection system. Input data signals are processed by a feedforwardequalization module and a decision feedback back equalization module.Decisions generated by the decision feedback equalization module isprocessed by an error detection module, which determines error eventsassociated with the decisions. The error detection module implements areduced state trellis path. There are other embodiments as well.

As mentioned above, error correction is an important aspect of datacommunication and processing. For example, as data are transmittedthrough a communication network, various types of interferences andnoises may cause errors in data transmission, and the receiving entityoften needs to remove interferences and noises before performing errorcorrection. For different types of interferences and noises, differenttechniques are used. For example, feed-forward equalization (FFE) boostsamplitudes of symbols surrounding transitions (e.g., from “0” to “1” orvice versa) and facilitates data processing. For example, by boostingsignal amplitude, the SNR can be improved. Decision-feedbackequalization (DFE) is effective in removing intersymbol interference(ISI) type of noises and errors, but it is often vulnerable to bursterrors. In various embodiments, the present invention provides maximumlikelihood sequence detection (MLSD) techniques that are particularlyuseful against DFE burst errors. As described in further details before,embodiments of the present invention provide error correction techniqueswith FFE, DFE, and MLSD blocks for signal processing.

The following description is presented to enable one of ordinary skillin the art to make and use the invention and to incorporate it in thecontext of particular applications. Various modifications, as well as avariety of uses in different applications will be readily apparent tothose skilled in the art, and the general principles defined herein maybe applied to a wide range of embodiments. Thus, the present inventionis not intended to be limited to the embodiments presented, but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

In the following detailed description, numerous specific details are setforth in order to provide a more thorough understanding of the presentinvention. However, it will be apparent to one skilled in the art thatthe present invention may be practiced without necessarily being limitedto these specific details. In other instances, well-known structures anddevices are shown in block diagram form, rather than in detail, in orderto avoid obscuring the present invention.

The reader's attention is directed to all papers and documents which arefiled concurrently with this specification and which are open to publicinspection with this specification, and the contents of all such papersand documents are incorporated herein by reference. All the featuresdisclosed in this specification, (including any accompanying claims,abstract, and drawings) may be replaced by alternative features servingthe same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

Furthermore, any element in a claim that does not explicitly state“means for” performing a specified function, or “step for” performing aspecific function, is not to be interpreted as a “means” or “step”clause as specified in 35 U.S.C. Section 112, Paragraph 6. Inparticular, the use of “step of” or “act of” in the Claims herein is notintended to invoke the provisions of 35 U.S.C. 112, Paragraph 6.

Please note, if used, the labels left, right, front, back, top, bottom,forward, reverse, clockwise and counter clockwise have been used forconvenience purposes only and are not intended to imply any particularfixed direction. Instead, they are used to reflect relative locationsand/or directions between various portions of an object.

FIG. 1A is a simplified block diagram illustrating an error correctionsystem according to embodiments of the present invention. This diagramis merely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. For example, the errorcorrection system illustrated in FIG. 1A is a portion of a communicationsystem that is responsible for processing received signals. For example,the communication system may use pulse-amplitude modulation (PAM)techniques for data transmission. Received signal x(u) is firstprocessed at FFE block 101. For example, FFE block 101 boosts theamplitude of incoming signals (e.g., data symbols in a PAM basedcommunication system). For example, by improving the amplitude ofreceived signal, FFE block 101 can effectively improve signal-noiseratio. At the same time, it is important for the FFE block 101 to notboost the incoming signals too much. If FFE block 101 applies too muchequalization, it may undesirably boost the amplitude of unwanted noise.For example, the amount of amplification by the FFE block 101 may bepredetermined and/or based on an assessment of the data signal x(u).

The output of FFE block 101 is the equalized signal x_(k) as shown inFIG. 1A. DFE block 102 removes ISI noise from the equalized signalx_(k). As described below, DFE block 102 (or in conjunction withadditional DFE blocks) can also provide preliminary decisions forcontrol loops, reflection cancellation module, and/or other functions.Unfortunately, DFE block 102 is not immune to errors. One type of errorfor which the DFE block 102 is particularly susceptible to is bursterrors, where error signal would bounce between two incorrect errors.For example, as DFE corrects an incorrect value of “+1” by subtracting“+1” from the output, the error state may change to “−1” due to overcorrection, and DFE output would oscillate between “+1” and “−1” beforesettling down (e.g., overcorrection in the subsequent turn would go onfor a while before burst errors are removed). Sometimes, this type oferror is also referred to as “bouncing” errors, as the error value wouldbounce back and forth. Depending on the signal quality and theimplementation of DFE, the burst error could take a while to removebefore dying out. For example, DFE response can be characterized by1+αD, with α≥0. Error events (e.g., burst errors) attributed to the DFEare typically Nyquist errors of type “+”, “+−”, “+−+”, etc. The outputof DFE block 102 is signal d_(k), which is processed by ee-MLSD block103.

The ee-MLSD block 103, among other features, is particularly suitablefor removing burst errors or error events attributed to DFE block 102.For example, MSLD block 103 specifically targets the structure of DFEerror. In various implementations, ee-MLSD block 103 uses trellis searchtechniques, where the trellis path includes two levels or two states.The traversal of trellis search is based on a maximum likelihooddetection calculation. In a specific implementation, linear response1+αD with PAM4 levels ±3 and ±1, a reduced state (e.g., two states)trellis path for ee-MLSD is used. After processing, ee-MLSD block 103provides data symbols for de-mapping at block 104, and the de-mappeddata are then processed by FEC block 105 for error correction. It is tobe understand that the FEC 105 can be implemented in various ways.

FIG. 1B is a simplified diagram illustrating a communication systemaccording to embodiments of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. Input data signal is firstprocessed by FFE block 101, which provides signal equalization tooptimize signal amplitude. The output of FFE block 101 is denoted asx_(k), which is processed by DFE block 102. The output of DFE block 102is used as a feedback loop at node 106. For example, output signal e_(k)at the node 106 is provided to other digital signal processing (DSP)functions, such as control loops or others. The output of DFE block 102is also used by reflection cancelation (RC) block 108. For example, RCblock 108 removes undesirable reflection that is common in high speedcommunication systems. Additional signal processing may be performed byDFE block 110. The ee-MLSD block 103, as explained above, specificallydetects error events associated with DFE block 102. For various legacyprocessing, block 111 as shown provides additional DSP features.

After equalization and error correction, data are de-mapped by de-mapblocks 104 and 112. For example, the de-mapping process may beassociated with PAM communication data and/or other data models. Theforward error correction (FEC) decoder module 105 then performs errorcorrection on the da-mapped data. Decoder module 105 as shown in FIG. 1Bincludes various processing blocks, but it is understood that othertypes of decoders or decoders with different configurations can be usedas well. It is to be appreciated that embodiments of the presentinvention provide a high level of flexibility, and the error detectionand correction techniques can be implemented into differentcommunication systems.

FIG. 1C is a simplified diagram illustrating an error detection moduleaccording to embodiments of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. Equalized signal (e.g.,processed by a FFE) x_(k) is first processed by the DFE block to detectISI errors. Preliminary decisions generate by the DFE block is denotedd_(k), and it is used by the error generator block 120, which outputs anerror signal denoted e_(k). For example, the error generator block 120determines the error signal by subtracting DFE decisions from theequalized signal received from the FFE. The ee-MLSD block detects eventerrors based on d_(k) and e_(k) as shown. After removing event errorsassociated with the DFE block, the ee-MLSD block output d_(k). Dependingon the implementation, MLSD processes can be expensive both inprocessing power and time. It is thus to be appreciated that embodimentsof the present invention provide reduced state trellis pathimplementation of MLSD that is efficient in terms of processing powerand time.

FIG. 1D is a simplified diagram illustrating an error detection modulewith an enable logic according to embodiments of the present invention.This diagram is merely an example, which should not unduly limit thescope of the claims. One of ordinary skill in the art would recognizemany variations, alternatives, and modifications. As shown in FIG. 1D,the ee-MLSD block is controlled by the enable logic block. For example,the enable logic block may determine (e.g., based on the amount of errore_(k)) that ee-MLSD processing is not needed, and the ee-MLSD blockcould then just let the data pass through. In certain embodiments, theenable logic determines whether to enable the ee-MLSD block based oninitial quality of the data signal. For example, the enable logic blockdetermines whether to enable the MLSD based on the quality of a datablock. In certain embodiments, the enable logic provides an enablesignal accompanying each data block, and the dynamic enable signal basedon the quality of each data block can save ee-MLSD power.

As explained above, MSLD removes errors events attributed to DFEdecisions. The output of the FFE block is denoted x_(k). The output ofDFE (preliminary DFE decisions) is denoted as d_(k). The error signal isdenoted e_(k). For the purpose of discussion, the DSP parallel factor isignored (i.e., time index k denotes UI index). As illustrated in FIG.1B, many error correction systems utilize DFE modules and errorgenerator blocks. DFE and error generator block provide controlinformation for the DSP control loops and preliminary inputs to the RCblock.

For the purpose of explanation, the target response (linear) isexpressed as g(D)=1+αD, and the DFE error events are expressed asϵ_(k)⊆{0,±1}. The DFE decision can thus be defined in Equation 1 below:d _(k) =d _(k) ^(ideal)−2ϵ_(k)  Equation 1:

-   -   Where d_(ideal) are the transmitted PAM (e.g., PAM4) symbols.

To explain the operation of DFE and MLSD, the error signal e_(k) isexpressed by Equation 2 below:e _(k) =x _(k)−(g*d)_(k)=2(g*ϵ)_(k) +n _(k),  Equation 2:

-   -   where n_(k) is the FFE output total/equivalent noise.

From the above equations, it can be proven that for a sequence x_(k) andDFE PAM4 decision d_(k), the maximum likelihood sequence detection(assuming n_(k) is additive white Gaussian noise, or AWGN) is equivalentto finding the error sequence ϵ_(k) that minimizes as expressed inEquation 3:

$\begin{matrix}{\min\limits_{\epsilon_{k}|{{d_{k} + {2\epsilon_{k}}} \in {{PAM}\; 4}}}{\sum\limits_{k}\left( {\frac{e_{k}}{2} - \left( {g*\epsilon} \right)_{k}} \right)^{2}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

In Equation 3, the minimization is conditioned on d_(k)+2ϵ_(k)∈PAM4 asnot all error events are valid given the DFE decision d_(k). Forexample, if d_(k)=3, then ϵ_(k) can only be either 0 (DFE made no error)or −1 (in which case the decision should be been +1 instead of 3). It isto be understood that while Equation 3 above uses PAM4 modulation as anexample, the ee-MLSD techniques can be used in other PAM-nimplementations, where n is an even integer.

For ease of notation, error signals are expressed as y_(k)=e_(k)/2. Itis to be appreciated that embodiments of the present invention simplifythe error minimization through exploiting prior knowledge of DFE eventerror. More specifically, DFE errors events (ϵ_(k)) for 0≤α≤1 areNyguist events as “+”, “+−”, “+−+”, “+−+−”, etc., and signed flippedversions thereof. With this knowledge, Equation 3 can be simplified toEquation 4 below:

$\begin{matrix}{\min\limits_{{\epsilon_{k} \in \mspace{14mu}{{Trellis}\mspace{14mu} T_{0}}}|{{d_{k} + {2\epsilon_{k}}} \in {{PAM}\; 4}}}{\sum\limits_{k}\left( {y_{k} - \left( {g*\epsilon} \right)_{k}} \right)^{2}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

The trellis T₀ in Equation 4 is illustrated in FIG. 2. FIG. 2 is asimplified state diagram illustrating a trellis state diagram accordingto embodiments of the present invention. This diagram is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. In searching the trellis path, the states of “0”,“+”, and “−” at the left side are the input states, and the outputstates “0”, “+”, and “−” are at the right side. The principle of thetrellis T₀ is expressed and explained in Equation 4. That is, the ruleof traversing the trellis path T₀ is determined using Equation 4, whichis an implementation of a maximum likelihood detection function.However, it is to be noted that having so many states as shown FIG. 2can be computationally expensive to implement.

To simplify the search, it is observed that trellis paths emanating fromstate “0” and ending at states “+” and “−” are 6 dB away from each otherin terms of Euclidean distance once one of the paths corresponds to thecorrect path (i.e., corresponding to the DFE error event). As the bestpossible MLSD SNR gain is less than 3 dB (e.g. for α=1), one can simplyfold the two states “+” and “−” under one state “E” without loss ofperformance.

FIG. 3 is a simplified state diagram illustrating a simplified trellisT₁ state diagram according to embodiments of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. The new trellis for DFEerror events is trellis T₁ illustrated in FIG. 3. The states “E_(i)” and“E_(o)” has an intrinsic variable c storing the sign of the error eventat time index k. The transition from state 0_(i) and state E₀ providesthe error event sign as sign of y_(k). By having only two input statesand two output states, the trellis path T₁ is reduced from a total ofsix states (as in trellis path T₀) to four states.

For example, the simplification of state graph can be proven by notingthat the expression min ϵ_(k)∈{±1} (y_(k)−ϵ)² is given byϵ_(k)=sign(y_(k)). The transition from state E_(i) to state E_(o) yieldsa sign flip of the error event ϵ.

To simplify the search process, the search process takes advantage ofthe Ferguson algorithm. More specifically, instead of usingkeeping/storing the path metrics for each state (i.e., “0”/“E”), theerror detection mechanism stores and updates the difference Δ betweenthe path metrics of each state. For example, as shown in FIG. 3, thedistance between state 0_(o) and state E0 is expressed by Equation 5below:Δ_(k) =P _(E) −P ₀  Equation 5:

It is to be appreciated that it is advantageous to use trellis with areduced number of states as illustrated FIG. 3. By having the reducednumber of states, the error detection mechanism eliminates the need forsquaring of the input signal-branch level to compute the branch metrics.Additionally, by reducing the number of states, the critical timing pathis reduced, where the add-compare-select (ACS) bottleneck is changed“add+compare+select” to mostly just “add+select”, as the compareoperation collapses to the sign of an updated value of the difference Δ.Furthermore, path metric normalization processes can be eliminatedthrough the use of limited fixed point representation of path metrics.There are other benefits as well, such as lowered power consumption.

FIG. 4 is a simplified diagram illustrating an ee-MLSD according to anembodiment of the present invention. This diagram is merely an example,which should not unduly limit the scope of the claims. One of ordinaryskill in the art would recognize many variations, alternatives, andmodifications. More specifically, FIG. 4 shows the branch metriccalculation and add-select (AS) unit for a simplified ML error trellissearch algorithm. It is to be appreciated that other implementations arepossible as well. As to be noted in FIG. 4, most functions are simply“add” functions (e.g., “A+B”) and “select” functions (e.g., between “C+”and “C−”). For example, by using AS unit instead of add-compare-select(ACS) unit, both hardware implementation and the computation process aresimplified. As an example, the ee-MLSD in FIG. 4 is specificallyimplemented for PAM4 data communication.

It is to be appreciated that error correction systems and methodsthereof provide many advantages over existing systems. The input signalto this simplified error event detector is simply y_(k)=e_(k)/2, whichhas reduced number of bits in its fixed-point representation compared toa conventional MLSD input. In a communication system, implementationsaccording to embodiments of the present invention can reduce the size ofbaseboard management controller (BMC) and the size of the inputbuffering required by block-based VD. By reducing the complexity oftrellis search (e.g., from FIG. 2 to FIG. 3), the number of branchmetrics and complexity thereof can be significantly reduced compared tothat of an MLSD with full states. To perform the trellis search, thereis no multiplication required to calculate the branch metrics, exceptfor one α*y_(k) per UI.

FIG. 5 is a graph illustrating simulation results comparing performanceof MLSD devices according to embodiments of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. The graph shows symbolerror rate (SER) on the y-axis in relation to the signal-to-noise ratio(SNR) on the x-axis, wherein the system is configured at 1+0.6D channelwith AWGN. DFE plot 501 is provided as a reference. As can be seen inFIG. 5, the SER measurements at different SNR levels for both aconventional full fledge MLSD and ee-MLSD (e.g., illustrated in FIG. 3)are almost the same, which means that the ee-MLSD can provideperformance very close to (if not identical) the full fledge MLSD.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. Therefore, the above description and illustrations should not betaken as limiting the scope of the present invention which is defined bythe appended claims.

What is claimed is:
 1. An error detection device comprising: a decision feedback equalizer (DFE) configured to remove intersymbol interference (ISI) noise from a data signal and generate DFE decisions; an error detector configured to detect error events associated with a sequence of data of the DFE decisions by performing maximum likelihood detections, the error detector being configured to generate an output error states; and an enable logic configured to generate a control signal for the error detector based on a quality of the data signal.
 2. The device of claim 1 further comprising a feedforward equalizer (FFE) configured to equalize the data signal.
 3. The device of claim 1 wherein the error detector removes burst errors associated with the DFE decisions.
 4. The device of claim 1 wherein the DFE comprises a reduced-state trellis path that comprises an intrinsic variable for storing signs of errors.
 5. The device of claim 1 wherein the error detector is configured to store signs associated with an input error state and generate an output error states by flipping the signs.
 6. The device of claim 1 further comprising a de-mapping module for processing the data signal.
 7. The device of claim 1 wherein the DFE comprises a reduced-state trellis path that comprises two input states and two output states.
 8. The device of claim 1 wherein the error detector is configured to flip signs using a reduced-state trellis path. 